Hill Climbing Primer

[ovrszd]

I've explained it more than once. I've also sat on tractors hitched low with the front wheels off the ground.

Yes you have. I've tried also. Seems we neither have used an example that is familiar to all. I still think if I could find a third member I might be able to display it in a manner that would be acceptable.

The pulling contest JD was a classic example but I'm afraid it was not accepted. I think we all need visuals. Your request for a force diagram was good but that seems to be unacceptable as well.

Oh well. It's all good.

 

[SPYDERLK]

I assume you are just trying to be funny.


But then,,,, if you don't know why the front tries to lift under power, you probably also do not know why the machine in fact does try to tip over sideways. This action is not visible on a vehicle without suspension but it is very noticeable in all others. Especially those with high torque engines such as big bore gassers or diesels. Go sit in a truckstop for 5 minutes watching the Semis come and go. You'll see both actions live and in person.


In an attempt to use examples that you might be familiar with, I also reference Super Stock cars at the drapstrip. Explain to me why they lift the left front tire first, then lighten the entire frontend and shift all that weight into traction to the rear tires???

A rigid body machine does not try to tip sideways. The trans output tries to rotate the body one direction, and the rear the other. The torques cancel. In the suspension case there is some windup before they cancel.
larry

 

[Egon]

(Originally Posted by msmith1wa
I am going to propose something that is not practical but takes what SPYDERLK is saying a little further.

Lets say there is an object that is to heavy or is theoretically immovable. Now lets dig a trench out from this object. Now fabricate a hitch that has the pull point below ground level. Now back the tractor up to the immovable object so that the trench is between the tires so that the hitch can be installed without dragging. Now pull on the immovable object with the tractor.

Will the tractor lift the front tires and tip over backwards? No it will not, in fact it will do just the opposite and actually force the front tires into the ground.)

---

If the tractor is stationary and the engine is turning over the front comes up. Sufficient traction, sufficient torque and sufficient load and the front comes up. Oh, the point of rotation is not the tire ground contact but rather around the axle. The tire is stationary as there is sufficient traction so no rotation there. The pinion force excerted on the ring gear has to be greater than the force of the load and it's lever arm. Sufficient torque.

It's like putting a big fellow on a short wrench with a very small Fellar on the long wrench!

A simple diagram would show how the forces are applied. All dem consolidated.forces within the tractor they figure right in with the outside force's.

Depending on the direction of engine rotation on back tire will have a little more down force on it.
.

---

 

[ovrszd]

A rigid body machine does not try to tip sideways. The trans output tries to rotate the body one direction, and the rear the other. The torques cancel. In the suspension case there is some windup before they cancel.
larry

I had to think about that for a moment...... I agree. That's why once it's moving the Semi settles back into it's normal position.

Why does the rear axle try to rotate sideways??

 

[SPYDERLK]

I've explained it more than once. I've also sat on tractors hitched low with the front wheels off the ground.

How low?

 

[SPYDERLK]

Torque on driveshaft wants to twirl it like a propeller.

 

[Egon]

How low?

Lower than high.

 

[ovrszd]

Torque on driveshaft wants to twirl it like a propeller.

Yep, or to put it into context in this conversation, the ring gear tries to walk the circle around the pinion gear, or "climb" it. Actually,,,,, after some thought,,,, crawl under it.

Kinda the same reaction that takes place when the pinion gear tries to walk the circle around the ring gear???

In regards to the axle housing it causes the axle housing to rotate sideways. In regards to the third member assembly it causes the axle housing to rotate backwards, which in turn causes the front of the vehicle to rise.

Pretty simple huh. Minus lengthy mathematical explanations.

 

[CalG]

Egon and my points are simply that there is no need for calculus or dynamics or statics or vectors or triangles or any other such methods of description. It's very simple. I was just curious if you could explain it. But now I'm not sure.

I scrounged thru my boneyard but couldn't find an intact third member. I'll check at my Son's shops and if I find one I can explain it all with 30 seconds of video, no charts, graphs, vectors or formulas. Just simple logic.

Wait,.... Egon is the one asking for vector diagrams....

I did dig through some of my scrap.
Two open differentials, one from a garden tractor complete with three speed transmission. and the other from a golf cart. Unfortunately, neither is "ring and pinion". and neither has a removable cover or a pumpkin to pull out.

If there is confusion regarding why engines rock, the front tire lifts or the rear squats, or why there is a traction bias (weight transfer) to one rear corner of an accelerating vehicle fitted with a "typical" solid axle rear end, I'm afraid there is a gulf between us.

How would you ever describe the resolution of forces on an excavatore?, or even a bridge? Does F=ma do anything for you? For me, the equation highlights the gravity constant, turning "mass" into weight ;-)

Don't let this come off as "personal", the conversation is stimulating.

 

[SPYDERLK]

(Originally Posted by msmith1wa
I am going to propose something that is not practical but takes what SPYDERLK is saying a little further.

Lets say there is an object that is to heavy or is theoretically immovable. Now lets dig a trench out from this object. Now fabricate a hitch that has the pull point below ground level. Now back the tractor up to the immovable object so that the trench is between the tires so that the hitch can be installed without dragging. Now pull on the immovable object with the tractor.

Will the tractor lift the front tires and tip over backwards? No it will not, in fact it will do just the opposite and actually force the front tires into the ground.)

---

If the tractor is stationary and the engine is turning over the front comes up. Sufficient traction, sufficient torque and sufficient load and the front comes up. Oh, the point of rotation is not the tire ground contact but rather around the axle. The tire is stationary as there is sufficient traction so no rotation there. >>>The pinion force excerted on the ring gear has to be greater than the force of the load and it's lever arm. <<< Sufficient torque.

It's like putting a big fellow on a short wrench with a very small Fellar on the long wrench!

A simple diagram would show how the forces are applied. All dem consolidated.forces within the tractor they figure right in with the outside force's.

>>Depending on the direction of engine rotation on back tire will have a little more down force on it.<<
.

---

>>> Thats just it. It cant happen when the pullpoint is below tire contact. Both the propulsion lever and the pull [load] lever bear equal force ; one pushing forward, the other exactly offseting that push by pulling back. The pull lever is longer so the net torque is to tip the tractor forward. The ring gear is factored into the push lever. Theres no other effect in a steady state or statioanary pull. Acceleration or a hill would introduce COM effects.<<<

>>All side tip forces would remain as if the tractor is off. Drive and driven torque are equal and opposite.<<

 

[CalG]

Yep, or to put it into context in this conversation, the ring gear tries to walk the circle around the pinion gear, or "climb" it. Actually,,,,, after some thought,,,, crawl under it.

Kinda the same reaction that takes place when the pinion gear tries to walk the circle around the ring gear???

In regards to the axle housing it causes the axle housing to rotate sideways. In regards to the third member assembly it causes the axle housing to rotate backwards, which in turn causes the front of the vehicle to rise.

Pretty simple huh. Minus lengthy mathematical explanations.

When will you describe the condition of "locked brakes" or axle shaft welded to the housing /bearings with these same simple terms?

The "forces" at the ring and pinion will be EXACTLY the same. Consider that the operator has a very good clutch foot and will not stall the engine. Or better, it's a HST or even a slush box in your daddy's Olds.

You must have done this when you were a young man. We called them "power burn outs" There was a lot of tension on a lot of parts, but I never saw the front end come up ;-)

I did see some s**T eat'in grins however! ;-)

 

[ovrszd]

Wait,.... Egon is the one asking for vector diagrams....

I did dig through some of my scrap.
Two open differentials, one from a garden tractor complete with three speed transmission. and the other from a golf cart. Unfortunately, neither is "ring and pinion". and neither has a removable cover or a pumpkin to pull out.

If there is confusion regarding why engines rock, the front tire lifts or the rear squats, or why there is a traction bias (weight transfer) to one rear corner of an accelerating vehicle fitted with a "typical" solid axle rear end, I'm afraid there is a gulf between us.

How would you ever describe the resolution of forces on an excavatore?, or even a bridge? Does F=ma do anything for you? For me, the equation highlights the gravity constant, turning "mass" into weight ;-)

Don't let this come off as "personal", the conversation is stimulating.

You are simply an imaginary person on the Internet. I don't take anything you say personal, unless you direct it that way. Such as when Larry blatantly said I was wrong. That was personal.

I applaud your search for a third member. Would have saved me shooting and posting a video. But actually I think we are going to get there without the video. Larry is almost arguing my case as we speak. He's just not quite realized it yet.

You say you understand why engines rock but twice I've asked you to explain it to me and you've responded with resolution of forces on an excavator and F=ma formulas. I just asked for a simple explanation. Like I asked Larry for a simple explanation why the axle housing tries to rotate sideways when power is applied. He answered with a very simple and accurate description, driveshaft trying to rotate the housing like a propeller. Which absolutely made my case concerning why the front of the vehicle rises when same power is applied.

It's all good.

 

[ovrszd]

When will you describe the condition of "locked brakes" or axle shaft welded to the housing /bearings with these same simple terms?

The "forces" at the ring and pinion will be EXACTLY the same. Consider that the operator has a very good clutch foot and will not stall the engine. Or better, it's a HST or even a slush box in your daddy's Olds.

You must have done this when you were a young man. We called them "power burn outs" There was a lot of tension on a lot of parts, but I never saw the front end come up ;-)

I did see some s**T eat'in grins however! ;-)

I was trying to be nice and just let the welded axle shaft issue die of it's own causes. Who cares what happens when the axle shaft is welded to the housing???? Really,,,,, who cares????? How could that possibly have anything to do with this discussion???? What functionality could a vehicle with welded axle shafts possibly have???

But I'm a nice guy. So here goes. You are ABSOLUTELY RIGHT. There will be no lifting force on the front of the vehicle if the axle shafts are welded to the housing or the brakes are held tight enough to hold the vehicle. Still have no idea what that's got to do with anything. But you are right......

Oh,,,,, I still do smokey burnouts with locked rear end and 38"x12.5" tires.

 

[CalG]

Why the engine rocks?

The crank shaft has mass and is ACCELERATING when the throttle is opened. Not simply rotating, but changing it's angular momentum. Oh! acceleration can be both + and minus, speed up or slow down.

The engine block has mass and is called on to provide the restoring force, equal and opposite the spinning crackshaft mass it contains. Or friend "Alfred E." NEWTON popularized the notion that for every action there must be an equal and opposite reaction. F=ma there it is, "Math never sleeps".


Think if the engine were floating in the marginal gravity of space when the throttle was opened. Rocking would not do the animation justice. It would be all out spinning.
But, if the crankshaft were not changing the velocity of it's mass, that is, only rotating at a steady rate, the entire system would come to some sort of equalibrium all in proportion to the relative masses envolved.

The rocking here on earth is just the elastic nature of the engine mounts and frame rails showing their "spring rate". The amplitude of the rocking has everything to go with the stiffness of the engine mounts and the CoG of the engine assembly. This rocking may be subdivided into engine balance factors , rocking couples etc. but those are not the subject here.

Did you know that the acceleration is different for the con rod as the crank passes over TDC than when it passes BDC? "thrown rods" nearly always happen at BDC .

A humorous aside. Do you know what the engineering unit for "rate of change of acceleration" is termed?

ready.....

It's a JERK! a detail we all seem to be quite well studied in from time to time ;-)

 

[CalG]

I was trying to be nice and just let the welded axle shaft issue die of it's own causes. Who cares what happens when the axle shaft is welded to the housing???? Really,,,,, who cares????? How could that possibly have anything to do with this discussion???? What functionality could a vehicle with welded axle shafts possibly have???

But I'm a nice guy. So here goes. You are ABSOLUTELY RIGHT. There will be no lifting force on the front of the vehicle if the axle shafts are welded to the housing or the brakes are held tight enough to hold the vehicle. Still have no idea what that's got to do with anything. But you are right......

Oh,,,,, I still do smokey burnouts with locked rear end and 38"x12.5" tires.

What difference? That simple detail demonstrates that a "climbing pinion" does not "lift" the front end of any tractor.

 

[SPYDERLK]

Yep, or to put it into context in this conversation, the ring gear tries to walk the circle around the pinion gear, or "climb" it. Actually,,,,, after some thought,,,, crawl under it.

Kinda the same reaction that takes place when the pinion gear tries to walk the circle around the ring gear???

In regards to the axle housing it causes the axle housing to rotate sideways. In regards to the third member assembly it causes the axle housing to rotate backwards, which in turn causes the front of the vehicle to rise.

Pretty simple huh. Minus lengthy mathematical explanations.

Except that one of those is output for appropriate resolution at ground reference. The other is not output - being totally resolved in the body.

As for suspension side tip - it has to be there any time there is torque in the drive train. It just isnt noticeable in most cases because its too small. Just me sitting in my car is like a 400ftlb tip urge and you cant see a result. Stabilizer bars are a help but they cant do it all. Ten of thousands of foot pounds in lo gear on a semi tractor is definitly noticed. The thousand or two in a steady cruise doesnt cause enuf tip to see. Youll see it downgearing on hills tho as the suspension unloads and reloads at a higher torque level.

 

[SPYDERLK]

What difference? That simple detail demonstrates that a "climbing pinion" does not "lift" the front end of any tractor.

It can if theres no load and the wheels are frozen in place. The tractor wants to turn the axle but the axle wont so the tractor will go around if it.can. This is much different than a load causing tip. It is concievable that net tire rotation can be backward relatve to ground, ... Also different than a load point configuration that wont allow tip.
larry

 

[CalG]

It can if theres no load and the wheels are frozen in place. The tractor wants to turn the axle but the axle wont so the tractor will go around if it.can. This is much different than a load causing tip. It is concievable that net tire rotation can be backward relatve to ground, ... Also different than a load point configuration that wont allow tip.
larry

SPYDERLK Did you miss the detail that the brakes were firmly applied? or the axle shaft welded to the housing?

In this exchange, the tires could be cast in concrete and there will be no different result.

The example is to demonstrate that forces seen within the tractor unit do not manifest external weight shifting unti "the rubber meets the road".

 

[CalG]

It can if theres no load and the wheels are frozen in place. The tractor wants to turn the axle but the axle wont so the tractor will go around if it.can. This is much different than a load causing tip. It is concievable that net tire rotation can be backward relatve to ground, ... Also different than a load point configuration that wont allow tip.
larry

SPYDERLK Did you miss the detail that the brakes were firmly applied? or the axle shaft welded to the housing?

In this exchange, the tires could be cast in concrete and there will be no different result.

The example is to demonstrate that forces seen within the tractor unit do not manifest external weight shifting unti "the rubber meets the road".

 

[Egon]

Wait,.... Egon is the one asking for vector diagrams....

I did dig through some of my scrap.
Two open differentials, one from a garden tractor complete with three speed transmission. and the other from a golf cart. Unfortunately, neither is "ring and pinion". and neither has a removable cover or a pumpkin to pull out.

If there is confusion regarding why engines rock, the front tire lifts or the rear squats, or why there is a traction bias (weight transfer) to one rear corner of an accelerating vehicle fitted with a "typical" solid axle rear end, I'm afraid there is a gulf between us.

How would you ever describe the resolution of forces on an excavatore?, or even a bridge? Does F=ma do anything for you? For me, the equation highlights the gravity constant, turning "mass" into weight ;-)

Don't let this come off as "personal", the conversation is stimulating.

Slug fest!